This invention relates to fluorometers and, more particularly, it concerns a low-cost and yet highly effective optical system for a dual channel, ultraviolet-visible, fluorometer in an immunoassay instrument and an associated method of fluorescence spectroscopy.
Fluorometers have gained wide acceptance for clinical analysis of blood and other biological fluids. Conventionally, fluorometers employ an optical system to subject a fluid sample, or a sample containing a fluorescent dye or tag material, to light energy at a first wavelength and cause emission of fluorescent light at a longer wavelength from the sample. The intensity of fluorescent emission is indicative of the presence or quantity of a substance in the sample under investigation. Because the amount of light absorbed and emitted by such biological fluid samples is low, conventional fluorometers are equipped with either one or both of a high output ultraviolet light source and a photomultiplier tube in order to achieve reliable test results.
High output ultraviolet light sources such as xenon arc lamps or lasers are not only expensive, but also suffer from drawbacks such as producing excessive heat, causing irreversible damage to specimens, creating noise, bleaching fluorescent tag materials, and requiring complex and expensive control systems. While it is known in the art to use a less expensive, relatively low ultraviolet output, broadband light source, such as a tungsten halogen lamp, and filter the lamp output with an ultraviolet transmitting bandpass filter, the resulting filtered radiation is of such a low level that the fluorescent light emitted by the sample is difficult to detect. Heretofore, the difficulty of fluorescent light detection has been addressed exclusively by the use of an extremely sensitive photomultiplier tube to detect the low levels of sample emitted fluorescence. While providing for radiation detection even at the photon counting level, photomultiplier tubes are expensive and fragile and necessitate relatively complex control circuitry.
In light of the foregoing, there is a need for an improved optical fluorometer system which provides the desired analysis without requiring the use of high ultraviolet output light sources and photomultipliers.